﻿// This is an open source non-commercial project. Dear PVS-Studio, please check it.
// PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com

// ReSharper disable CheckNamespace
// ReSharper disable ClassNeverInstantiated.Global
// ReSharper disable CommentTypo
// ReSharper disable IdentifierTypo
// ReSharper disable InconsistentNaming
// ReSharper disable StringLiteralTypo
// ReSharper disable UnusedParameter.Local

/* Concat.Enumerable.cs --
 * Ars Magna project, http://arsmagna.ru
 */

#nullable enable

namespace AM.Memory.Collections.Linq;

internal sealed class ConcatExprEnumerable<T>
    : IPoolingEnumerable<T>
{
    private IPoolingEnumerable<T>? _src, _second;
    private int _count;

    public ConcatExprEnumerable<T> Init
        (
            IPoolingEnumerable<T> src,
            IPoolingEnumerable<T> second
        )
    {
        _src = src;
        _count = 0;
        _second = second;
        return this;
    }

    public IPoolingEnumerator<T> GetEnumerator()
    {
        _count++;
        return Pool<ConcatExprEnumerator>.Get().Init
            (
                this,
                _src!.GetEnumerator(),
                _second!.GetEnumerator()
            );
    }

    private void Dispose()
    {
        if (_count == 0)
        {
            return;
        }

        _count--;
        if (_count == 0)
        {
            _src = default;
            _second = default;
            Pool<ConcatExprEnumerable<T>>.Return (this);
        }
    }

    internal class ConcatExprEnumerator : IPoolingEnumerator<T>
    {
        private ConcatExprEnumerable<T>? _parent;
        private IPoolingEnumerator<T>? _src, _second;
        private bool _first;

        public ConcatExprEnumerator Init
            (
                ConcatExprEnumerable<T> parent,
                IPoolingEnumerator<T> src,
                IPoolingEnumerator<T> second
            )
        {
            _parent = parent;
            _src = src;
            _second = second;
            _first = true;
            return this;
        }

        public bool MoveNext()
        {
            if (_first)
            {
                if (_src!.MoveNext())
                {
                    return true;
                }

                _first = false;
            }

            return _second!.MoveNext();
        }

        public void Reset()
        {
            _first = true;
            _src!.Reset();
            _second!.Reset();
        }

        object IPoolingEnumerator.Current => Current!;

        public T Current => _first ? _src!.Current : _second!.Current;

        public void Dispose()
        {
            _parent?.Dispose();
            _parent = default;
            _src?.Dispose();
            _src = default;
            _second?.Dispose();
            _second = default;
            Pool<ConcatExprEnumerator>.Return (this);
        }
    }

    IPoolingEnumerator IPoolingEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}
